Propylene polymers and propylene-olefin copolymers are inexpensive and are excellent in mechanical properties, heat resistance, chemical resistance and water resistance and thus have been used in a wide range of fields. For example, it is occasionally practiced to form a coat layer on the surface of a molded product made of a propylene polymer. A propylene-based polymer has no polar groups in its molecule and thus is defective in that it normally has a low polarity and can difficultly undergo coating or adhesion. Accordingly, in order to improve this defect, (1) various approaches such as chemical treatment of the surface of the molded product of propylene-based polymer with a chemical agent or the like and oxidation treatment of the surface of the molded product by corona discharge treatment, plasma treatment, flame treatment or the like have been attempted. However, these approaches not only require a special apparatus but also leave something to be desired in the improvement of coatability or adhesion.
Further, (2) an approach involving the undercoating of the surface of the molded product of propylene-based polymer with a chlorinated polypropylene has been known. The formation of this chlorinated polypropylene coat layer makes it possible to improve the subsequent coatability of the molded product. In other words, since a chlorinated polypropylene is normally soluble in a hydrocarbon solvent such as toluene and xylene, can be easily applied to the molded product, exhibits a good adhesion to a propylene-based polymer which is a base material and has its molecule provided with a polarity derived from carbon-chlorine bond, the coatability and adhesion of a propylene-based polymer can be improved. It has also been known that a modified chlorinated polypropylene obtained from the chlorinated polypropylene by the graft copolymerization of polar monomers has a better effect of improving coatability and adhesion.
However, the chlorinated polypropylene or modified chlorinated polypropylene to be used as an undercoating agent is a resin containing a large amount of chlorine and thus is environmentally undesirable. This is because the use of vinyl chloride resins has recently brought forth a social issue over the harmful matters generated by recycling or incineration thereof. It has been keenly desired to develop substitute resins free of halogen such as chlorine for chlorinated polypropylene as in vinyl chloride resins.
However, no halogen-free propylene-based polymer resins having a good solubility in an organic solvent as well as a good adhesion have heretofore been found.
An object of the present invention is to provide a novel propylene-based polymer which can provide a propylene-based polymer as a base material with a good adhesion and coatability even if it is free of halogen such as chlorine.